1. Field of the Invention
This invention relates to a developing device for use in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus.
2. Related Background Art
In an image forming apparatus utilizing an electrophotographic system, an electrostatic latent image is formed on an image bearing member and it is developed and visualized as a toner image, and the toner image is transferred onto a transfer material to thereby obtain an image.
As the above-described developing method, generally there are a one-component developing method using a one-component developer comprising only a magnetic toner, and a two-component developing method using a two-component developer comprising magnetic particles (magnetic carrier) and a toner. However, the one-component developing method has the merit that the construction of a developing device is simpler and the maintenance thereof is easy, and at present, various one-component developing devices based on this one-component developing method are proposed and put into practical use.
There is also proposed a developing method using a non-magnetic one-component developer comprising only a non-magnetic toner, as shown in Japanese Patent Laid-Open No. 58-116559, and in order to cope with the recent tendency toward the coloring of images, there is put into practical use a developing device which can provide colored images of high quality and which is moreover low in cost and compact.
As an example, a non-magnetic one-component developing device is shown in FIG. 7 of the accompanying drawings. In the developing device of FIG. 7, a cylindrical non-magnetic developing sleeve 1 rotatable in the direction of arrow is installed as a toner carrying member in a developing container 3 containing therein a non-magnetic toner which is a one-component developer, and a toner supplying and collecting roller 14 and a regulating blade 13 as a developer regulating member abut against the developing sleeve 1.
The toner supplying and collecting roller 14 comprises a mandrel 14a of SUS or like material and an elastic member 14b of urethane foam or like material formed on the outer peripheral surface of the mandrel 14a, and is rotated while frictionally contacting with the developing sleeve 1 to thereby supply the non-magnetic toner contained in the developing container 3 to the surface of the developing sleeve 1. Also, it has the action of scraping off any non-magnetic toner which has not contributed to the development in a developing portion opposed to a photosensitive drum, not shown, and has been returned into the developing container 3 with the rotation of the developing sleeve 1 from the surface of the developing sleeve 1.
The regulating blade 13 comprises a support member 13a formed of phosphor bronze or like material and attached to the developing container 3 and an elastic member 13b of urethane rubber or like material adhesively secured to the support member 13a, and the elastic member 13b elastically bears against the surface of the developing sleeve 1 to thereby regulate the toner born (carried) on the developing sleeve 1 and form it into a thin toner layer and also impart frictional charging charges to the toner.
By the above-described construction, the developing device can well form a thin layer of charged non-magnetic toner on the developing sleeve 1 and supply it for the development of an electrostatic latent image formed on the surface of the photosensitive drum and thus, the good development of the latent image has become possible.
In the above-described non-magnetic one-component developing device, however, the imparting of charges to the toner is effected by the frictional contact of the toner on the developing sleeve 1 with the regulating blade 13 or the developing sleeve 1 when it passes the regulating blade 13. Therefore, charges can be well imparted to the toner of the layer-like toner on the developing sleeve 1 which passes the vicinity of the regulating blade 13 and the developing sleeve 1, but it is difficult to impart sufficient charges to the toner present in the interior of the toner layer.
Therefore, in some cases, a bias occurs in the distribution of the charge amount in the thin toner layer formed on the developing sleeve 1 by regulation and thus, uncharged toner and reversed toner exist in the toner layer. The uncharged toner and reversed toner cause poor (bad) images such as fogged image.
To eliminate the uncharged toner and reversed toner and impart a predetermined or greater amount of charges to all the toner in the toner layer, it is necessary to make the pressure of contact of the regulating blade 13 with the developing sleeve 1 high, make the amount of toner passing there small and increase the chance of contact of the toner with the regulating blade 13 and the developing sleeve 1.
However, to form an image of sufficient density, a certain degree of toner amount is necessary and there is also a limit to making the toner layer thin by an increase in the pressure of contact of the regulating blade 13. An increase in the pressure of contact of the regulating blade 13 also leads to the problem that the mechanical load applied to the toner becomes very great.
Also, the toner supplying and collecting roller 14 bearing against the developing sleeve 1 frictionally contacts with the latter to thereby effect the supply of fresh toner to the developing sleeve 1 and the collection of any toner remaining after development and therefore, depending on the location of the toner supplying and collecting roller 14 and the direction of rotation of the roller 14, there has been a case where the toner remaining after development cannot be completely collected.
If the toner remaining after development is not collected but remains residual on the developing sleeve 1, the residual toner again passes between the regulating blade 13 and the developing sleeve 1 and is charged. When by this recharging, the toner receives excessive charges, the force with which the toner adheres to the developing sleeve 1 increases and therefore, it is difficult for the toner to separate from the developing sleeve 1 in the developing portion and the toner may sometimes be returned into the developing container 3 without being used for development.
If in such a manner, the toner remaining on the developing sleeve 1 after development after passes the toner supplying and collecting roller 14 and the regulating blade 13 while remaining restrained on the surface of the developing sleeve 1, the shape of the toner is gradually changed by a mechanical load received each time and the accumulation of heat generated at that time, and an extraneous additive or the like controlling the amount of charges and fluidity of the toner is buried into the toner and thus, the toner is deteriorated.
Such deteriorated toner cannot obtain a desired charging characteristic and fluidity, thus causing many problems during an image forming process.
When for example, the amount of the deteriorated toner increases on the developing sleeve 1, the supply of fresh toner may be hindered and the amount of toner on the developing sleeve 1 after regulation may decrease and the developing property of the toner may be reduced. Also, even if the once deteriorated toner is collected into the developing container 3 by the toner collecting roller and thereafter is again supplied to the developing sleeve 1, the desired charging characteristic and fluidity cannot be obtained and therefore, a good developing property is not obtained and further, poor (bad) transfer such as hollow characters is caused during transfer.
Further, when the deteriorated toner is fused on the surface of the contacting portion of the regulating blade 13 and the surface of the developing sleeve 1, a bad coat such as streaks occurs to the toner layer on the developing sleeve 1. Also, the imparting of charges to the toner newly supplied to the developing sleeve 1 is hampered and thus, uncharged toner may be conveyed to the developing portion to thereby cause a bad image such as fog and unevenness.
On the other hand, if the frictional contact of the toner supplying and collecting roller 14 with the developing sleeve 1 continues for a long time, the wear and injury of the roller 14 itself and the clogging or the like of the toner may occur and the role as the toner supplying and collecting roller 14 will become insufficient and the roller 14 may sometimes become incapable of effecting a good supply of toner.
As described above, the developing device using the non-magnetic toner is simple in construction and yet can effect good development, but lacks the durability and stability of the toner and the developing device and has only been utilized chiefly in developing devices of the cartridge type in which the developing device is bodily interchanged during the supply of a toner, and has not much adopted in developing devices of a type in which when necessary, a toner is supplied as in a copying apparatus.
It is an object of the present invention to provide a developing device which makes image formation of high dignity in which uncharged toner does not contribute to development possible.
It is another object of the present invention to provide a developing device in which a load applied to a toner during the supply of the toner to a developing sleeve and during the imparting of charges to the toner is remarkably reduced to thereby realize a low stress coat of toner and which is usable as a developing device of a toner supply type for a long period of time.
It is still another object of the present invention to provide a developing device comprising:
(a) a developer bearing member for bearing a developer thereon and conveying the developer to an image bearing member;
(b) a developer supplying member for supplying the developer to the developer bearing member; and
(c) a charging member for discharging between the charging member and the developer supplying member to thereby charge the developer borne on the developer supplying member;
wherein the developer charged by discharging between the developer supplying member and the charging member is supplied to the developer bearing member.
Other objects and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.